Stable carbon isotope ratio analysis (SCIRA) of honey for undeclared presence of cane or corn sugars has been available for 20 years. Its use with domestic and imported honeys is reviewed. Six years of data from the internal standard isotope ratio analysis (ISCIRA) method support its worldwide validity for honey analysis. The ISCIRA database of pure honeys has been increased from 64 U.S. samples to 224 by addition of data from Germany, United Kingdom, Mexico, Italy, and Spain. ISCIRA analyses of 131 commercial honeys from the United States, Mexico, and Spain found that 17 are adulterated. Analyses of 303 Chinese honeys proves that they should have carbon isotope values similar to honeys from other areas, contrary to claims that the observed differences are intrinsic because of the variability of environmental conditions and of plants used in honey production in China. Addition of corn or cane (C4) sugars to honeys in amounts that do not produce a δ13C value greater than -23.5%o for the mixture cannot be detected by the original 1978 SCIRA procedure. Such adulteration however is detected by ISCIRA procedure from the δ13C value of the protein contained in the honey, which shows the isotopic composition of the honey before addition of C4 sugars. Fortythree percent of 98 honeys received in the United States in 1994-1997 with δ13C < -23.5%o were suspected and found to be adulterated.
Mn(II)-catalyzed oxidation by molecular oxygen is considered a relevant process for the environmental fate of aminopolyphosphonate chelating agents such as aminotrismethylene phosphonate (ATMP). However, the potential roles of Mn(III)ATMP-species in the underlying transformation mechanisms are not fully understood. We combined kinetic studies, compound-specific stable carbon isotope analysis, and equilibrium speciation modeling to shed light on the significance of such Mn− ATMP species for the overall ATMP oxidation by molecular oxygen. The fraction of ATMP complexed with Mn(II) inversely correlated with both (i) the Mn(II)-normalized transformation rate constants of ATMP and (ii) the observed carbon isotope enrichment factors (ε c -values). These findings provide evidence for two parallel ATMP transformation pathways exhibiting distinctly different reaction kinetics and carbon isotope fractionation: (i) oxidation of ATMP present in Mn(III)ATMP complexes (ε c ≈ −10 ‰) and (ii) oxidation of free ATMP by such Mn(III)ATMP species (ε c ≈ −1 ‰) in a catalytic cycle. The higher reaction rate of the latter pathway implies that aminopolyphosphonates can be trapped in catalytic Mn-complexes before being transformed and suggests that Mn(III)ATMP might be a potent oxidant also for other reducible solutes in aqueous environments.
The recent development of reliable GC/qMS methods for δ 37 Cl compound-specific stable isotope analysis (CSIA) paves the way for dual carbonchlorine isotope analysis of chlorinated ethenes and thus allows deeper insights into underlying transformation processes/mechanisms. A two-point calibration is indispensable for the precise and correct conversion of raw data to the international δ 37 Cl SMOC scale. The currently available calibration standards for tetrachloroethylene (PCE) span only a very narrow range from À2.52‰ (EIL2) to +0.29‰ (EIL1), which is considerably smaller than observed δ 37 Cl isotope enrichment in (bio-)transformation studies (up to 12‰).
Methods:We describe the preparation and evaluation of a new 37 Cl-enriched PCE standard to avoid bias in δ 37 Cl CSIA arising from extrapolation beyond the calibration range. The preparation comprised: (i) partial PCE reduction by zero-valent zinc in a system of PCE, ethanol (initial volume ratio 3/5) and trace amounts of water followed by (ii) liquid-liquid extraction and (iii) a subsequent fractional distillation to purify the 37 Cl-enriched PCE.Results: The obtained PCE (PCE enriched ) showed a purity of 98.8% (mole fraction) and a δ 37 Cl SMOC value of +10.8 ± 0.5‰. The evaluation of an experimental dataset with and without extrapolation showed no significant variation.
Conclusions:The new PCE standard (PCE enriched ) expands the calibration range to 13.3‰ (previously 2.8‰) and thus prevents potential bias introduced by extrapolation beyond the calibration range.
| INTRODUCTIONCompound-specific stable isotope analysis (CSIA) of light elements (e.g., δ 13 C and δ 15 N) has become an indispensable tool for numerous applications within environmental sciences including (contaminant) source identification, detection and quantification of in situ (bio-) transformation as well as identification of reaction mechanisms. The isotopic enrichment during transformation is caused by kinetic isotope effects: lower vibrational energies of bonds containing a heavy isotope result in slower reaction rates when a bond containing a heavy isotope is cleaved. 1 As a result, progressive transformation results in an accumulation of heavy isotopes within the reactant. The
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